Obstructive sleep apnea is a disorder characterized by recent pharyngeal collapse during sleep leading to arousals, sleep disruption, autonomic activation and blood gas derangements. (1) Substantial literature suggests that the pathophysiology ob obstructive sleep apnea related to deficient pharyngeal anatomy (7) and state-related changes in the control of musculature. However, additional data indicate that mechanisms other than muscle control play an important role in apnea pathogenesis with falling lung volume being an important possibility. Numerous studies in animals and a few in humans suggest that long volumes influence upper airway geometry, muscle function and in OSA patients, the severity of their disease. (15-23) . In this grant, we propose a series of studies to: 1) Characterize the influence of lung volumes on upper airway dilator muscle function, airway mechanics and airway geometry in normal individuals and patients with obstructive sleep apnea, both awake and sleep. 2) Define the impact of advancing age, gender and obesity on the relationships between lung volume and upper airway muscle control, pharyngeal mechanics and airway geometry.